Prone to homesickness, Cavill recalls crying to his mom at boarding school "four times a day," admitting he became an "easy target" before landing his first role in The Count of Monte Cristo at age 17.

"I lost one and a half stone (21 pounds) and I wasn't Fat Cavill anymore," he says with satisfaction.

Although acting brought out Cavill's hidden confidence, he won't divulge any details on his post-Superman weight. He admits he's "not eating 5,000 calories a day anymore" to maintain his bulky superhero bod, but he isn't comfortable sharing any specifics.

"I will say I was a lot bigger as Superman," he confesses. "A lot bigger. I'm not saying how much. It's modesty about the weight—I've always been worried about my weight—but I also don't want to invite that debate: Henry weighs this, so he's the perfect Superman. Or, Henry doesn't weigh this, and therefore he's not believable in the role."

Another defining moment during Cavill's boarding school days? His chance encounter with Russell Crowe, who now plays his father Man of Steel (and is equally fond of the British star).

"He was on campus filming Proof of Life," Cavill recalls. "Everyone was standing in a semicircle, and I thought, 'We look ridiculous, staring like he's some kind of prize pony.' So I walked up and said, 'Hi, my name is Henry. I'm thinking of becoming an actor. What's the acting world like?"

Shortly after, he received a package from Russell containing snacks, a rugby jersey, a CD of the actor's band and a signed note: "It said, 'Dear Henry, a journey of a thousand miles begins with a single step.'"

And years later, he reminded his costar of the defining moment: "I told him, 'I was the fat one who didn't ask for your autograph.' He looked at me blankly, and then he actually remembered."

Funny how life works. But safe to say "Fat Cavill" has the last laugh.